Towards endothelial-cell-directed cancer immunotherapy: In vitro expression of human recombinant cytokine genes by human and mouse primary endothelial cells

Recent studies have demonstrated the feasibility of cytokine gene transfer to enhance the antitumor activities of host immune cells. Endotheiial cells forming the vascular supply of tumors may be useful vehicles for the delivery of cytokine molecules in order to effect tumor immunotherapy. In order to determine whether primary endothelial cells can express cytokine transgenes efficiently, we constructed two retroviral vectors containing a cDNA encoding either recombinant human interleukin-la (rhlLla) or recombinant human interleukin-2 (rhlL-2), called LNCIL-la and LNCIL-2 respectively, and studied the expression of the two cytokines in vitro in non-immortalized endothelial cells. Human umbilical vein endothelial cells (HUVEC) transduced with LNCIL-la or LNCIL-2 secreted 1.8-33 ng/106 cells/24 h and 40-246.7 ng/106 cells/24 h of biological active rhIL-la and rhlL-2 respectively. Mouse microvascular endothelial cells (MMEC) transduced with LNCIL-la and LNCIL-2 secreted 1.5 ng/106 cells/24 h and 5.8-24.7 ng/106 of biologically active rhIL-la and rhlL-2 proteins respectively. Cocultivation of HUVEC/IL-2 and MMEC/IL-2 with normal human bone marrow cells generated potent cytotoxic activity against K562, Daudi and other cell targets in a 51Cr-release assay. While IL-2 transgene-expressing HUVEC and M M EC retained their normal morphology, rhIL-la transgene expression inhibited the growth and altered the morphology of both HUVEC and M M EC in culture. The cytokine-gene-transduced endothelial cells retained other endothelial cell features, including uptake of acetylated low-density lipoprotein (Ac-LDL) and expression of von Willebrand factor, and were euploid as shown by flow cytometry. These results demonstrate that endothelial cells, by sustaining the production of biologically active rhlL-2 at levels that are sufficient for the activation of potent cytotoxic lymphocyte activity, may be useful agents for cancer gene therapy.